1. Field of the Invention
The present invention relates to a semiconductor device, a light emitting apparatus and an electronic device. The present invention particularly relates to a semiconductor device having thin film transistors of an inverted-stagger structure on an insulating substrate, a light emitting apparatus in which the semiconductor devices are applied and an electronic device equipped with the light emitting apparatus.
2. Description of the Related Art
In recent years, a flat-type display such as a liquid crystal display device, an organic electroluminescence (EL) display, a plasma display and the like are used as displays and monitors of portable devices such as a cellular phone, a digital camera and the like and electronic devices such as a television, a personal computer and the like to a great extent.
In such flat-type display, an active matrix drive method is generally applied and a panel structure in which thin film transistor devices using silicon thin films as channel layers are provided on an insulating substrate such as glass is applied in general as the display panel and the driver thereof.
As for the thin film transistor to be provided on the insulating substrate, various types of device structures are known. For example, JP10-289910 and the like describe the thin film transistor having a channel stopper type inverted-stagger structure (or a bottom gate structure) in which a gate electrode is disposed on the lower layer side of a semiconductor layer, a channel protecting layer is provided to cover over the region which is to be the channel layer of the semiconductor layer and a source electrode and a drain electrode are provided on the semiconductor layer and a portion of the source electrode and the drain electrode overlapped on the channel protecting layer.
Further, for example, JP2001-264818 and the like describe that misalignment of the source electrode and the drain electrode occurs with respect to the channel protecting layer when forming the source electrode and the drain electrode on the semiconductor layer by patterning in the above described thin film transistor having the inverted-stagger structure (or the bottom gate structure).
When the misalignment of the source electrode and the drain electrode occurs with respect to the channel protecting layer in the above described thin film transistor having the inverted-stagger structure, the ON currents of the thin film transistors vary. Therefore, when such thin film transistors are applied as the display panel, the switching device of the driver and the driving element of the flat-type display, the display image quality is degraded and the product yield is reduced due to the misalignment.
More in particular, in the case in which the thin film transistors are used as the driving elements in the pixels each of which including the current driven light emitting device (for example, organic EL device) and the driving element for driving the light emitting device to emit light, when the current values of the light emitting drive currents which are to be supplied to the light emitting devices vary due to the misalignments, the pixels cannot be driven to emit light at the desired luminance tone. Therefore, for example, in the display including the display panel in which a plurality of pixels (light emitting devices) are two dimensionally arranged, the entire screen cannot be made to emit light at a uniform luminance. Therefore, the display image quality is degraded and the product yield is reduced.